This invention relates to a process for the oligomerization of olefins.
In many fields of polymerization processing, in order to obtain the desired properties and production throughput, it is conventional to stop the polymerization at a low degree of polymerization. Such industrial oligomerization process require the establishment of satisfactory systems for providing the olefins as well as for the oligomerization itself.
In the case of olefin recovery in steam cracking plants, the yields of the individual olefins are present on the basis of the thermodynamics or the reaction kinetics. A substantial increase in the yield of a specific olefin, while employing constant cracking conditions can be achieved only by recycling the products. But in the case of thermal cracking of feedstocks containing hydrocarbons, besides ethylene and propylene, other olefins are produced such as butenes, which cannot be recycled, since they would lead to a rapid coking of the cracking tubes in the steam cracking plant, which would in turn result in a loss of hydrocarbons.
Another application of olefin oligomerization reactions relates to the use of residual gases from fluidized catalytic cracking (FCC) processes. FCC residual gases are conventionally converted to fuel components in costly processes by alkylation or oligomerization liquid phase reactions. With the introduction of lead-free gasoline, such products have become of increasing importance as blend components. The liquefied FCC residual gases are released from the light components under pressure in a fractionating tower and are then reacted in the presence of a catalyst such as sulfuric acid, phosphoric acid or hydrogen fluoride. The reaction products are fractionated in a fractionating tower into a polymer or alkylate as bottoms product and light components as overhead product. The bottoms product is fractionated throughout the boiling range, with the residual gases being recycled to the process. This process is described in greater detail in "Hydrocarbon Processing", Vol. 60, No. 9, September 1981, pp. 134-138.
Disadvantages of the processes known so far are that the acids catalysts employed must be separated thereby requiring expensive processes in part caused by substantial environmental and corrosion problems. When dissolved catalysts (homogeneous catalysts) are used, the dissolved catalysts must also be separated from the product.